1. Field of the Invention
The invention in general relates to the formation of sonar beams, and particularly to an arrangement utilizing CCD's and a SAW device for forming multiple beams for side looking sonar operation.
2. Description of the Prior Art
The chirp Z-transform is a Fourier transform technique utilized in the sonar field for forming multiple beams. The technique is used in conjunction with an elongated multi-element transducer array wherein the output signals from the elements are provided to a charge coupled device (CCD). The CCD is read out at a certain rate and is mixed with a frequency chirp signal, that is a signal whose frequency varies linearly with time. The resultant signal is then "de-chirped" in a convolver consisting of a surface acoustic wave (SAW) device, the output signal of which is detected, the detected signal constituting the multiple beam signals.
The multiple beams formed extend radially from the middle of the multi-element transducer array and are useful for forward looking sonar applications for imaging a target area forward of the apparatus.
The radially positioned beams however are not conducive to side looking sonar applications where parallel beams are desired for imaging a target area laterally of the apparatus. The present invention accomplishes this beam formation for side looking sonar application.